The present invention relates to a variable valve operating system equipped with a first variable mechanism capable of controlling lift characteristics of an engine valve such as an intake valve or an exhaust valve, and second variable mechanism capable of controlling a valve-open and/or valve-close timing.
As is generally known, there have been proposed and developed various variable valve operating systems that can enhance an engine operating performance by enhancing a degree of freedom of valve operating characteristics by way of a combination of a variable lift mechanism capable of variably adjusting a valve lift characteristic of an intake valve and a variable valve timing mechanism capable of variably adjusting valve-open and/or valve-close timing characteristics.
However, in such conventional variable valve operating systems, there were insufficient studies of a measure to counter in case at least one of the variable lift mechanism and the variable valve timing mechanism fails with an internal combustion engine in operation, thereby causing several problems, that is, mechanical problems such as the interference between at least two of a piston, an intake valve, and an exhaust valve, in particular a problem of remarkably reduced engine performance.
That is to say, in variable valve operating systems disclosed in Japanese Patent Provisional Publication No. 4-287809 and Japanese Utility Model Provisional Publication No. 3-99860, a variable lift mechanism and a variable valve timing mechanism both use hydraulic pressure as an energy source. Therefore, in presence of a hydraulic system failure, for example, in presence of a failure in an electromagnetic switching valve disposed in the middle of a hydraulic circuit or in presence of a failure in a hydraulic equipment included in a hydraulic pressure control system, a malfunction of the variable lift mechanism and a malfunction of the variable valve timing mechanism occur. In this case, it is difficult to variably control both of a valve lift and a valve timing. As a result of this, it is impossible to produce a sufficient engine performance, and also there is a possibility of remarkably reduced engine performance due to particular engine operating conditions.
Additionally, even when a hydraulic system failure does not occur, owing to a high viscosity resistance at low oil temperature conditions such as during an engine start-up period, it is difficult to insure a satisfactory operation of each of the variable lift mechanism and the variable valve timing mechanism. Due to the high viscosity resistance as well as a long length of a hydraulic pressure passage, a delay in hydraulic pressure supply from a hydraulic pump to each of the variable lift mechanism and the variable valve timing mechanism occurs. Owing to such a system malfunction, there is a technical problem of a reduced control response for each of the variable lift mechanism and the variable valve timing mechanism to a change in the engine operating condition for a while after starting.
As an additional prior art, Japanese Patent Provisional Publication No. 8-177434 also discloses a variable valve operating system.
Roughly speaking, the previously-noted variable valve operating system is equipped with a valve lift control mechanism capable of variably controlling a cam lift of an intake valve (serving as an engine valve) or a cam lift of an exhaust valve (serving as an engine valve) by selectively switching from one of a low-speed cam and a high-speed cam (both provided on a camshaft) to the other depending on engine operating conditions, and a valve timing control mechanism capable of variably controlling a valve-open and/or valve-close timing by changing a relative angular phase between the camshaft and a crankshaft depending on the engine operating conditions.
Additionally, the above-mentioned system is also equipped with a control mechanism provided to avoid the interference between the intake valve and the exhaust valve by forcibly switching to the low-speed cam by means of the valve-lift control mechanism in presence of a failure in the previously-noted valve timing control mechanism, or by controlling the valve-open and/or valve-close timing of the engine valve by means of the valve timing control mechanism so that a center of operation of a valve lift moves away from a top dead center in presence of a failure in the previously-noted valve lift control mechanism.
In the aforementioned variable valve operating system, as discussed above, it is possible to avoid the mechanical problem such as the interference between the intake valve and the exhaust valve in presence of a failure in each of the valve lift control mechanism and the valve timing control mechanism. However, in case either one of the control mechanisms fails, the system functions to forcibly switch to the low-speed cam by means of the valve lift control mechanism or to control a valve-open and/or valve-close timing so that the center of operation of a valve lift moves away from the top dead center by virtue of the valve timing control mechanism. As a matter of course, a valve overlap through which both the intake and exhaust valves are open together becomes reduced. Therefore, in a high engine-speed operating range, the engine power output tends to reduce, and thus it is difficult to produce a satisfactory engine performance.
In order to accomplish the aforementioned and other objects, according to the invention as claimed in claim 1, a variable valve operating system of an internal combustion engine comprises a first variable mechanism capable of variably controlling at least a lift characteristic of an engine valve depending on an engine operating condition, and a second variable mechanism capable of variably controlling at least a valve-open and/or valve-close timing characteristic of the engine valve depending on the engine operating condition, characterized in that the first variable mechanism is driven by an electric actuator, whereas the second variable mechanism is driven by hydraulic pressure of working fluid, and in that the system inhibits the second variable mechanism from being driven and allows only the first variable mechanism to be driven within an operating range from engine start operation to a time when a temperature of the working fluid reaches a predetermined temperature value, and the system allows both the first and second variable mechanisms to be driven from a time when the temperature of the working fluid exceeds the predetermined temperature value.
In accordance with the previously-noted invention, a power source of the first variable mechanism is different from a power source of the second variable mechanism. Except the engine starting period, even in case either one of an electric system and a hydraulic system failsi the other variable mechanism cannot be affected, and thus at least one variable mechanism can be driven normally. Therefore, it is possible to prevent the engine performance from lowering. Furthermore, during the engine starting period a valve lift is generally adjusted to a small amount, and therefore there is no problem of the previously-discussed interference even in presence of the system failure.
Additionally, even when both the variable mechanisms are driven, actuation of the second variable mechanism, using hydraulic pressure as a power source, is inhibited during the engine starting period, and is allowed from the time when the temperature of working fluid reaches the predetermined temperature value. Thus, for a while from the engine starting, it is possible to enhance. various engine performances, such as a startability, owing to high-response lift control of the first variable mechanism. Additionally, after a rise in the temperature of working fluid, it is possible to largely enhance the engine performances by way of a combination of both the first and second variable mechanisms.
According to the invention as claimed in claim 2, a valve lift of the engine valve is controlled to a minimum lift substantially corresponding to a substantially zero-lift position during engine cranking corresponding to an initial stage of engine starting, and then the valve lift of the engine valve is variably controlled so that the valve lift increases according to a rise in engine speed.
Therefore, during the engine cranking corresponding to the initial stage of engine starting, the hydraulic-pressure driven second variable mechanism cannot be driven, and in lieu thereof the valve lift of the engine valve can be controlled to the minimum lift substantially corresponding to a substantially zerolift position by means of the first variable mechanism. Thus, it is possible to provide a smooth engine-speed rise characteristic. Further, the valve lift tends to increase according to a rise in engine speed, thereby enhancing a gas exchange efficiency, and consequently insuring a good-startability.
According to the invention as claimed in claim 3, the above-mentioned first variable mechanism comprises a drive shaft having a drive cam formed on an outer periphery thereof, and an oscillating cam being oscillatingly supported on a pivot and acting to open and close the engine valve by way of oscillating motion thereof, and a rocker arm rotatably linked at one end to the drive cam and rotatably linked at the other end to the oscillating cam, and a center of the oscillating motion of the rocker arm being variably controlled by means of a control cam.
In accordance with the previously-noted invention, the valve lift can be continuously varied by rotating the control cam, and additionally it is possible to set a variable width of valve lift to a greater value. The system of the invention can provide a sufficient engine performance even in presence of a failure in each of the variable mechanisms as well as in absence of the failure in each of the variable mechanisms.
Additionally, owing to the use of the control cam, a phase of the valve lift uniquely changes according to a change in the valve lift, but the second variable mechanism, capable of varying the phase of the drive shaft, is combined with the first variable mechanism, and thus it is possible to correct the previously-noted unique changes in the phase of the valve lift. As a result of this, it is possible to provide a satisfactory engine performance in the absence of the failure in each of the variable mechanisms.
According to the invention as claimed in claim 4, the first variable mechanism comprises a drive shaft having a drive cam formed on an outer periphery thereof, and an axis of the drive cam being eccentric to an axis of the drive shaft, a link arm rotatably at one end linked to an outer periphery of the drive cam, a rocker arm rotatably linked at one end to the other end of the link arm, and a center of oscillating motion being variably controlled by means of a control cam, an oscillating cam acting to open and close the engine valve, a link member mechanically and rotatably linking the oscillating cam to the other end of the rocker arm, and an electric actuator controlling a rotational position of the control cam by rotating the control cam by means of a control shaft responsively to the engine operating condition.
In accordance with the previously-noted invention, by means of the link member, it is possible to limit a maximum range of oscillating motion of the oscillating cam within. a range of oscillating motion of the rocker arm. Thus, even in a high engine speed range, it is possible to certainly prevent a jumping phenomena, such as excessive oscillation and excessive jumping motion. Therefore, it is possible to avoid collision between the oscillating cam and the rocker arm, occurring due to movement of the oscillating cam into and out of contact with the rocker arm, thus preventing occurrence of hammering noise, and also preventing the accuracy of valve-lift control from lowering. In particular, in the high engine speed range, it is possible to stabilize the engine performance.
According to the invention as claimed in claim 5, a variable valve operating system of an internal combustion engine comprises a first variable mechanism capable of variably controlling at least a lift characteristic of an engine valve depending on an engine operating condition, a second variable mechanism capable of variably controlling at least a valve-open and/or valve-close timing characteristic of the engine valve depending on the engine operating condition, a position detection means for detecting a current actuated position of at least one of the first and second variable rimechanisms, and a control means being responsive to a failure position of the at least one of the first and second variable mechanisms, detected by the position detection means, for controlling movement of the other variable mechanism within a predetermined range when the at least one of the first and second variable mechanisms fails.
In accordance with the previously-noted invention, for example, when the first variable mechanism fails in a predetermined engine operating range, the position detection means detects a failure position of first variable mechanism, and then its informational signal is output into the control means, and thereby the control means can control can control the second variable mechanism within the predetermined range capable of avoiding a mechanical interference between engine valves as much as possible, responsively to the failure position of the first variable mechanism. Hitherto, the conventional system functioned to forcibly switch or control to a low-speed cam by means of the first variable mechanism. Therefore, according to the system of the invention, it is possible to insure a satisfactory engine performance depending on the engine operating condition, as much as possible.
According to the invention as claimed in claim 6, a variable valve operating system of an internal combustion engine comprises a first variable mechanism capable of variably controlling at least a lift characteristic of an engine valve depending on an engine operating condition, a second variable mechanism capable of variably controlling at least a valve-open and/or valve-close timing characteristic of the engine valve depending on the engine operating condition, a position detection means for detecting a current actuated position of the second variable mechanism, and a control means being responsive to a failure position of the second variable mechanism, detected by the position detection means, for controlling movement of the first variable mechanism within a predetermined range when the second variable mechanism fails.
According to the invention as claimed in claim 7, a variable valve operating system of an internal combustion engine comprises a first variable mechanism capable of variably controlling at least a lift characteristic of an engine valve depending on an engine operating condition, a second variable mechanism capable of variably controlling at least a valve-open and/or valve-close timing characteristic of the engine valve dependinng on the engine operating condition, a position detection means for detecting a current actuated position of the first variable mechanism, and a control means being responsive to a failure position of the first variable mechanism, detected by the position detection means, for controlling movement of the second variable mechanism within a predetermined range when the first variable mechanism fails.
In accordance with the previously-noted invention as recited in claims 6 and 7, in the same manner as the invention as recited in claim 5, when one of the first and second variable mechanisms fails, by means of the control means it is possible to control the other variable mechanism as much as possible, and continuously or intermittently within a predetermined range capable of avoiding a mechanical interference between an engine valve and a piston and a mechanical interference between an intake valve and an exhaust valve, responsively to the failure position of one variable mechanism. Therefore, it is possible to prevent the engine performance from lowering, while avoiding mechanical problems.
According to the invention as claimed in claim 8, the above-mentioned first variable mechanism comprises a drive shaft having a drive cam formed on an outer periphery thereof, and an oscillating cam being oscillatingly supported on a pivot and acting to open and close the engine valve by way of oscillating motion thereof, and a rocker arm rotatably linked at one end to the drive cam and rotatably linked at the other end to the oscillating cam, and a center of the oscillating motion of the rocker arm being variably controlled by, means of a control cam.
In accordance with the previously-noted invention, the valve lift can be continuously varied by rotating the control cam, and additionally it is possible to set a variable width of valve lift to a greater value. The system of the invention can provide a sufficient engine performance even in presence of a failure in each of the variable mechanisms as well as in absence of the failure in each of the variable mechanisms.
Additionally, owing to the use of the control cam, a phase of the valve lift uniquely changes according to a change in the valve lift, but the second variable mechanism, capable of varying the phase of the drive shaft, is combined with the first variable mechanism, and thus it is possible to correct the previously-noted unique changes in the phase of the valve lift. As a result of this, it is possible to provide a satisfactory engine performance in the absence of the failure in each of the variable mechanisms.
According to the invention as claimed in claim 9, the first variable mechanism comprises a drive shaft having a drive cam formed on an outer periphery thereof, a link arm rotatably at one end linked to an outer periphery of the drive cam, a rocker arm rotatably linked at one end to the other end of the link arm, and a center of oscillating motion being variably controlled by means of a control cam, an oscillating cam acting to open and close the engine valve, a link member mechanically and rotatably linking the oscillating cam to the other end of the rocker arm and limiting a maximum range of oscillating motion of the oscillating cam within a range of oscillating motion of the rocker arm, and an electric actuator controlling a rotational position of the control cam by rotating the control cam by means of a control shaft responsively to the engine operating condition.
In accordance with the previously-noted invention, by means of the link member, it is possible to limit the maximum range of oscillating motion of the oscillating cam within the range of oscillating motion of the rocker arm. Thus, even in a high engine speed range, it is possible to certainly prevent a jumping phenomena, such as excessive oscillation and excessive jumping motion. Therefore, it is possible to avoid collision between the oscillating cam and the rocker arm, occurring due to movement of the oscillating cam into and out of contact with the rocker arm, thus preventing occurrence of hammering noise, and also preventing the accuracy of valve-lift control from lowering. In particular, in the high engine speed range, it is possible to stabilize the engine performance.